Saute onion, and prepare stuffing mix according to package directions--set aside.
In a medium sauce pan, melt butter and then add flour. Stir until bubbly, then cook one minute. Slowly add in milk, stirring continuously to avoid lumps.
Add chicken, celery, onion, salt and pepper.
Cook and stir for 5-10 minutes, until chicken is done and celery is starting to get tender.
Pour mixture into an 8×8-inch casserole dish. Top with stuffing.
Bake, uncovered, at 350 degrees for 30-35 minutes.
Recipe by Faithful Provisions at https://faithfulprovisions.com/cooking-101-farmhouse-chicken/